textproduct: Rapid City

KEY MESSAGES

- Cold front crosses the region this evening into tonight, taking about 30 degrees off our temperatures for Sunday and increasing humidities; still no significant precipitation.

- Generally mild and dry weather resumes for a portion of next week with elevated to near-critical fire weather conditions quickly returning; cool-down possible for the end of the week.

UPDATE

Issued at 944 PM MDT Sat Mar 21 2026

Cold front has moved through the area this evening, over performing with wind gusts. Winds will quickly die down this evening. Passing upper level impusle will support a few showers overnight, with the best chances across northeast WY into the Black Hills early Sunday. Cooler Sunday with a cloudy start and clearing by afternoon. Frontal boundary will waver over the region early next week with warming trend through Wed, although a backdoor cool front may settle further south into the region Tues, with cooler conds possible on the SD Plains then. Bumped up highs on Wed toward the NBM 50 percentile as another unseasonably warm day is expected with highs in the 80s at most of the SW third to half once again.

DISCUSSION

(This Evening Through Saturday) Issued at 145 PM MDT Sat Mar 21 2026

Dominant high pressure ridging over the western US will somewhat break down and give way to more of a zonal nature to the flow over the next week, placing northwestern Wyoming and western South Dakota in a SLIGHTLY more active storm track...at least enough to more frequently break up our stretches of heat and critical fire weather, even if very little precipitation relief remains on the horizon. Our first big change will be the long-advertised cold front crossing the CWA from north to south this evening and tonight, switching gusty winds into the north and bringing in cooler temperatures and slightly higher humidities. A few showers remain likely with the front (and we massaged PoPs up slightly and broadbrushed them out a bit over NBM guidance to capture the range of solutions offered by the 12z HREF CAMs), yet we still don't expect anyone to exceed 0.10 inches of QPF from this system. We also bumped winds up a bit from this afternoon into the first half of tonight on either side of the front (blending the ongoing forecast with a hint of the NBM 75th percentile). The western ridge tries to amplify just slightly through the first half of the upcoming week bringing back some warming and drying (and a quick return of elevated to near-critical fire weather conditions), but another trough will likely bring another noticeable cool-down and a few light showers Thursday, with cooler temps continuing into next weekend. 500mb height ensemble cluster analysis offers outstanding agreement through Thursday, but then starts to show some large potential differences in the orientation of our synoptic flow (ridging? zonal? northwest?) by the weekend as well as uncertainty around the potential amplification of troughing upstream moving into the Pacific NW and northern Rockies. Thus, overall forecast confidence is currently low Friday onward. We're still NOT, however, seeing signs of any significant precipitation-makers in our future.

AVIATION

(For the 12Z TAFS Through 12Z Monday Morning) Issued At 504 AM MDT Sun Mar 22 2026

MVFR/LCL IFR conditions in low stratus and scattered showers will continue to move across northeastern WY and western SD through this morning. Conditions will improve to VFR areawide by early afternoon.

FIRE WEATHER

Issued At 145 PM MDT Sat Mar 21 2026

A combination of very warm temperatures in the 80s and 90s, low relative humidities of 8 to 20 percent, winds gusting as high as 35- 40 MPH (direction will vary depending on location), and ongoing drought will result in another day of widespread critical fire weather conditions through this evening across much of northeastern Wyoming and western South Dakota. A RED FLAG WARNING remains in effect for most of the region through 9 PM MDT this evening, and was expanded earlier this morning to include the Butte County area. This area will be one of the first to see the cold front move in this evening supporting predominantly north/northeast winds and eventually higher RH values, but most guidance still achieves at least 15-20 percent min RH, and conceptually it seems likely that there will be some overlap of low RHs with critically breezy conditions for a few hours this afternoon/evening (current sfc obs are approaching 20 percent RH as of this writing in the western part of the zone). Along similar thinking with the cold front...confidence in achieving Red Flag criteria is high for both winds and RH across northeastern Wyoming and the southwestern South Dakota Plains, but confidence in RHs drops along the I-90 corridor and points northward as current obs carry slower drying on an east to north wind depending on location, with the front on the way. All- in-all...certainly not confident at all in clearing any zone from the warning early this afternoon, and we encourage everyone to take precautions to avoid sparking any new fires in this environment. Winds will also be quite gusty along and behind the front this evening into tonight with a more definitive switch to north across our entire forecast area, and wetting rains are NOT expected anywhere with shower activity along the front.

Looking ahead, Sunday will still be a bit breezy, especially across the northwestern South Dakota Plains, but afternoon RH values look to hold more in the 20-35 percent range, so some temporary improvement there along with cooler high temperatures in the 50s to near 60. A drying/warning trend returns, however, into mid-week, with elevated to near-critical fire weather conditions returning to portions of the region each day. Winds look to strengthen the most out toward Wednesday and Thursday, with relatively low forecast confidence thereafter.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.